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The semi-dry SDA process has many advantages:
The spray drying absorption process
As the hot, untreated flue gas is introduced into the absorber module via the flue gas dispersers for optimum flue gas distribution, it comes into contact with the highly reactive absorbent sprayed by the rotary atomizer. In the semi-dry flue gas desulfirization process, an efficient contact between the flue gas and atomized absorbent slurry is established which allows for rapid mass transfer of acidic components from the flue gas into the liquid alkaline absorbent.
The alkaline absorbent neutralizes the absorbed acid (SO2 + Ca(OH)2 -> CaSO3/CaSO4 + H2O). The desired reaction product is formed while water is evaporated simultaneously. A fraction of the dried end-product drops to the bottom of the absorber chamber and is discharged, while the main part is taken to the downstream dust collector with the cooled flue gas, and removed from the now clean gas. The clean gas passes from the dust collector to the stack without re-heating.
The GEA Niro semi-dry FGD process uses slaked lime Ca(OH)2 as absorbent and produces a dry end-product mainly consisting of fly ash and various calcium compounds. The absorbent is either purchased directly as slaked lime or, more often and more economically, prepared from burned lime CaO on site. From a buffer tank, the slaked lime is pumped to the rotary atomizer by which it is atomized to droplets of less than 50 microns. By atomizing 1 litre of absorbent slurry, you obtain 1.5x1010 particles with a diameter of 50 microns equalling a total surface area of 120m2. Following the absorption of acidic components, the chemical reaction and the final drying, the end-product is separated from the gas phase as a powder and transported either to an end-product storage facility or recycled in the semi-dry process for improved utilization of excess absorbent.
The SDA technology features excellent performance for absorption of not only the primary pollutants like SO2 and HCl, but due to the combination of finely sprayed absorbent into the flue gas stream and the subsequent dust removal, pollutants like SO3, HF, etc. are almost completely removed. This allows for the use of carbon steel as construction material throughout the entire flue gas path. Other features of the GEA Niro semi-dry process are that it allows use of low quality process water, such as waste water or even sea water, and that the process generates no waste water.
The end-product from the process is a stable and dry powder and is used for a variety of purposes. The majority of the SDA product produced throughout the world is re-used in road construction, building materials, and for other purposes in the construction industry.
The unique implementation of spray drying technology for acid gas absorption was originally invented by GEA Niro in the 1970’s, and has ever since continuously been further developed and optimized to meet changing conditions and requirements. Hence, GEA Niro’s semi-dry process stands as an efficient, versatile and mature technology.
GEA Niro customizes our SDA process to fit the customer's needs and demands as well as meeting relevant environmental legislations. Well-proven features are among others peak control systems and activated carbon injection systems to ensure low mercury and dioxin emission.
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